Income tax systems in some countries follow primarily schedular models that classify income by type, match it with deductions from the same class, and compute a separate tax on each class. The United States income tax uses a global tax model under which it taxes citizens and permanent residents on their worldwide income without regard to source or character. The United States system is not purely global but includes schedular elements. This Article exposes embedded schedularity in the United States income tax in the three principal areas of investment income, personal services income, and tax free income. The Article tests whether that schedularity enhances or undercuts the tax principles of horizontal and vertical equity that underlie the development of both global and schedular tax systems in advanced economies. Horizontal equity is a straightforward principle and seems an indisputable precept. It requires that like taxpayers incur like tax burdens. The principle of vertical equity is more nuanced and departs from the principle that as one’s income increases, one can and should contribute ever larger percentages of that income to supporting governmental services. Vertical equity assumes that the wealthier one is, the less likely it is that an increased tax burden will diminish the individual’s welfare in any material way. Conversely, the less wealthy one is, the more likely it is that an increased tax burden will diminish the individual’s welfare materially. The vertical equity principle led to the development of the progressive rate structures. While the Article observes that Congress uses schedular elements to accomplish distributional policy goals, initially in order to protect progressivity, more recently schedularity has tended to increase overall regressivity in taxation. The Article concludes that United States taxation seems to be moderately schedular and that schedularity in the United States contributes to regressivity in taxation.
